Remove deprecated StringBuffer.add, addAll and addCharCode.

tests/compiler/dart2js/deprecated_features_test.dart

Index: tests/compiler/dart2js/deprecated_features_test.dart
diff --git a/tests/compiler/dart2js/deprecated_features_test.dart b/tests/compiler/dart2js/deprecated_features_test.dart
index 7c8bc58a98a8abdd9b49683ebf014c42556a95f5..b2aafa2fdda073804e7a2f66b6cd31f48116cd2d 100644
--- a/tests/compiler/dart2js/deprecated_features_test.dart
+++ b/tests/compiler/dart2js/deprecated_features_test.dart
@@ -16,12 +16,12 @@ main() {
     if (kind == Diagnostic.VERBOSE_INFO) return;
     if (identical(kind.name, 'source map')) return;
     if (uri == null) {
-      messages.add('$kind: $message\n');
+      messages.write('$kind: $message\n');
     } else {
       Expect.equals('main:${uri.path}', '$uri');
       String source = TEST_SOURCE[uri.path];
       Expect.isNotNull(source);
-      messages.add('$begin<${source.substring(begin, end)}>:${uri.path}:'
+      messages.write('$begin<${source.substring(begin, end)}>:${uri.path}:'
                    '$kind: $message\n');
     }
   }